Mass spectrometry comprises a broad range of instruments and methodologies that are used to elucidate the structural and chemical properties of molecules, to identify the compounds present in physical and biological matter, and to quantify the chemical substances found in samples of such matter.
Mass spectrometers measure the masses of individual molecules that have been converted to gas-phase ions, i.e., to electrically charged molecules in a gaseous state. The principal parts of a typical mass spectrometer are the ion source, mass analyzer, detector, and data handling system. In practice, solid, liquid, or vapor samples are introduced into the ion source where ionization and volatilization occur. To effect ionization, it is necessary to transfer some form of energy to the sample molecules. In most instances, this causes some of the nascent molecular ions to disintegrate into a variety of fragment ions. Both surviving molecular ions and fragment ions formed in the ion source are passed onto the mass analyzer, which uses electromagnetic forces to sort them according to their mass-to-charge ratios (m/z), or a related mechanical property, such as velocity, momentum, or energy. After they are separated by the analyzer, the ions are successively directed to the detector. The detector generates electrical signals, the magnitudes of which are proportional to the number of ions striking the detector per unit time. The data system records these electrical signals and displays them on a monitor or prints them out in the form of a mass spectrum, for example as a graph of signal intensity versus m/z. In principle, the pattern of molecular-ion and fragment-ion signals that appear in the mass spectrum of a sample, such as microorganism sample, constitutes a unique chemical fingerprint from which the sample's constituents can be deduced. The identification of microorganisms based upon their spectroscopic, spectrometric, and chromatographic characteristics would represent a useful method for the identification of microorganisms such as yeast, fungi, protozoa, and bacteria, including pathogenic organisms.
Since the discovery of typing whole cell bacteria by mass spectrometry (see e.g. Meuzelaar and Kistemaker, Anal. Chem. 45 (3): 587-590, 1973; and Meuzelaar et al., Biol. Mass Spectrometry, 1 (5): 312-319, 1973), numerous attempts have been made to automate the typing process, most recently using either pyrolysis mass spectrometry (PyMS) (Gutteridge and Schweppes, Meth. Microbiology, 19. ISBN 0-12-521519 3, Academic Press Limited, UK, 1987, Freeman et al., 1990, and Fenselau and Demirev, J. Med. Microbiol. 32, 283-286, 2002) or matrix-assisted laser desorption/ionization time-of flight mass spectrometry (MALDI TOF) (see e.g. Bright et al., J. Microbiol. Methods, 48 (2-3): 127-138, 2002; William et al., J. Am. Soc. Mass. Spectrom. 14 (4): 342-351, 2003; Keysa et al., Inf., Gen. and Evol. 4 (3): 221-242, 2004). However generating reproducible mass spectra from bacterial samples in a timely fashion at atmospheric pressure has remained problematic for many years. Furthermore, rapid pathogen identification to the subspecies level from bacteria to form a library of reproducible mass spectra has not been achieved, despite several attempts at various approaches (see e.g. Goodacre and Kell, Current Opin. in Biotechnol., 7, 1: 20-28, 1996; and Fenselau and Demirev, Mass Spectrometry Rev., 20, 4: 157-171, 2001). Thus, there is a need for new methods and devices that enable the pathogen identification using mass spectrometric analysis.